Normal murine bone morphometry: a comparison of magnetic resonance microscopy with micro X-ray and histology.

Abstract

The authors have devised a means to assess subtle changes in the structure of bone using magnetic resonance (MR) microscopy. MR microscopy was compared with micro X-ray and histology to analyze the structure of normal bone. Femurs of C57Bl/6 mice were examined ex vivo using differently orientated slices and pulse sequences on both a 9.4 and 11.7 T MR scanner, followed by micro X-ray and histology. A thresholding analysis technique was applied to MR images, to generate contour lines delineating the boundaries between bone and marrow. By MR microscopy, optimal correlation with histological "gold standards" was obtained using a longitudinal sectional versus a cross-sectional slice profile, a short echo time gradient-echo sequence versus a long echo time spin-echo sequence, and a higher field strength, 11.7 T versus 9.4 T. Gradient-echo images at 11.7 T were acquired with a maximum in-plane resolution of 35 microm. Our results demonstrate that the percent area of marrow increases and percent area of trabecular bone and cortical bone thickness decreases on moving from the epiphyseal growth plate to the diaphysis. These changes observed with MR microscopy correlate with the histological data, but did not correlate with micro X-ray data, which showed no trends. Our quantitative evaluation using MR microscopy was found to be an effective means to visualize the normal variation in bone microanatomy compared with a histological "gold standard", and was a superior means of quantification in comparison with micro X-ray.